The increase of the elderly population in the urban areas of Argentina is comparable to that of many North American and European cities. Consequently, the incidence of age-related neurological pathologies is becoming a problem of significant medical and economic impact for the country. In this context, the overall goal of the present proposal is to establish a long-term collaboration between the American and Argentine applicants, who share an interest in the potential of gene therapy for the treatment of neurodegenerative diseases. Three specific objectives are proposed: 1) To assess the performance of self-regulating adeno associated viral (AAV) vectors in the brain of old rats. These vectors harbor a reporter gene encoding humanized green fluorescent protein (hGFP) under the control of the tet-off or tet-on promoter system which can be turned off or on, respectively by administration of tetracycline (Tet) or certain Tet derivatives. The above vectors will be stereotaxically injected in the paraventricular, periventricular and arcuate nuclei, all of which contain dopaminergic (DA) neurons of known vulnerability to aging. 2) To assess the therapeutic efficacy of a self-regulating tet-off AAV vector harboring the gene for human glial cell line-derived neurotrophic factor (hGDNF), a potent neuroprotective molecule. The vector will be stereotaxically injected in the arcuate nucleus of 24-month old rats and 6 months later, its ability to prevent the normal age-related loss of hypothalamic tuberoinfundibular DA (TIDA) neurons will be assessed by quantitative immuno-histochemistry for DA neurons and ELISA for hGDNF. Serum PRL levels (an index of TIDA neuron function) will be monitored in the animals throughout the experiment. 3) To construct two self-regulating adenoviral vectors (RAd) harboring suicide genes under the control of the tet-off system. One of the RAds will harbor a hybrid suicide gene coding for a fusion protein between hGFP and HSV1 thymidine kinase (HSV1-TK), which retains fluorescence and HSV1-TK suicide activity. The other RAd will harbor the separate genes for HSV1-TK and hGFP under the control of a bi-directional Tet-off regulatory element. These two vectors, which are expected to be safer than non-regulatable counterparts, will be employed to treat experimental rat prolactinomas. Further to the above specific objectives, contacts with basic and clinical neuroscientists are planned in the US and Argentina in order to assemble a follow up research program focused on senile brain disorders.